Preinsulated pipe assembly and pipeline

ABSTRACT

A preinsulated pipe assembly and pipeline formed from a plurality of such assemblies. Each pipe assembly includes a pipe with a heater housing mounted thereon to form a cavity along the exterior of the pipe and a preformed insulation layer for insulating the pipe and the heater housing. A connecting assembly is used to join the pipe assemblies and form a pipeline. Pull means detachably connected to a heating element facilitates placement of the heating element in the heater housing cavities, and a pulling assembly attached to the heater element permits removal of the heater element after installation of the pipeline.

BACKGROUND OF THE INVENTION

The field of this invention is pipe assemblies and pipelines.

Pipelines in which heating elements or other thermal control apparatusare incorporated find many applications and frequently must be employedwhere freeze protection or thermal process control functions are to beaccomplished in a pipeline.

In the past, pipelines having conduits attached to a pipe and heatingelements disposed in the conduits were available. The conduit wasattached to the pipe and the pipeline was insulated at the installationsite. These installation operations in the field necessitatedtransporting large amounts of material, equipment, and manpower to thefield. The installation operations were frequently performed underdisadvantageous circumstances, resulting in high installation cost andsometimes poorly insulated pipelines.

Other pipelines had a permanently affixed heating element on the pipe.The heating elements were attached to the pipes at the installationsite, and the pipelines were insulated after the heating elements hadbeen affixed to the pipe. In addition, since the heating element waspermanently affixed to the pipe, the heating element could not bereplaced without difficulty and possible damage. Further, where suchpipelines were buried underground, the pipeline had to be at leastpartially uncovered before the task of replacing the heating elementcould even begin.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a new and improved pipeassembly and pipeline formed from a plurality of such assemblies.

With the pipe assembly of the present invention, a pipe with a fluidflow passage therethrough has a heater housing mounted on the pipeexterior. The heater housing forms a cavity along the pipe exterior forreceiving a heating element to heat fluids in the pipe flow passage. Apreformed insulation layer extends around the pipe and heater housingunit to insulate them. A jacket is also preferably provided at theexterior of the insulation layer to protect the insulation layer.

Preferably, the heater housing is a channel shaped or concave member andis mounted with the pipe so that its open channel or concavity isoriented toward the pipe exterior to form the heater housing cavity.This structure enhances the heat transfer characteristics of the pipeassembly because the heating element disposed in the cavity comes indirect contact with the pipe exterior and a relatively large area of thepipe exterior is exposed to the heater housing cavity.

A plurality of such pipe assemblies are joined to form a pipeline whichmay either be placed above ground or buried beneath the earth's surface.A connecting assembly is provided with this invention to permit theassemblies to be joined. Each of the assemblies which form the pipelineinclude a preformed insulation layer; that is, the insulation layer ismounted on each assembly as the assembly is constructed so that theassemblies are transported to the pipeline installation site aspreinsulated units. By providing such a preformed insulation layer, mostof the insulating operations which previously had to be done in thefield are performed at a manufacturing plant or other location where theassemblies are constructed. Only the connecting assembly need beinsulated in the field when the pipeline of the present invention isinstalled. Consequently, use of production techniques for insulating thepipe assemblies is possible, and most of the pipeline insulation work isperformed under the controlled environmental conditions found inmanufacturing plants.

With the pipeline assemblies connected and in place at the theinstallation site, the heating element is placed in the heater housingcavity without disturbing or removing the preformed insulation layer oneach pipe assembly. Pull lines are provided with the heating element. Byapplying a force to these pull lines, the heating element is moved intothe heater housing cavity. Terminal stations are also provided with thepresent invention to permit access to portions of the heating elementafter it is installed in the heater housing cavity. These terminalstations are used to connect the heating element with a source of powerand to permit testing and inspection of the heating element. Shouldreplacement of the heating element become necessary, a pull assemblyattached to the heating element is provided so that operator can removethe heating element from the heater housing cavity. Since the heatingelement is not permanently affixed to either the heater housing or thepipe, the operator may simply disconnect the heating element from theterminal stations and exert a force on the pulling assembly to move theheating element out of the heater housing cavity. Thus, the heatingelement may be removed from the pipeline without making it necessary todismantle either the pipeline insulation or the heater housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional end view of one embodiment of the pipe assembly ofthe present invention.

FIG. 2 is a sectional end view of a second embodiment of the pipeassembly of the present invention.

FIG. 3 is a plan view illustrating portions of the connecting assemblyused with the pipeline of the present invention.

FIG. 4 is a perspective view illustrating the connection of two pipeassemblies of the present invention.

FIG. 5 is schematic representation of a pipeline formed according to thepresent invention.

FIG. 6 is a partial sectional view of one embodiment of a terminalstation of the present invention.

FIG. 7 is a partial sectional view of the pulling assembly of thepresent invention.

FIG. 8 is a perspective view of a second embodiment of a terminalstation used with the present invention.

FIG. 9 is a perspective view illustrating the installation of heatingelements in the pipeline.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings, a letter P designates generally the pipeline of thepresent invention which is formed from a plurality of novel preinsulatedpipe assemblies A, each of which includes a preformed insulationlayer 1. The assemblies are joined together with a connecting means D toform the pipeline P. A heating means E, removably mounted with theconnected pipe assemblies A, extends between terminal stations T whichare provided at spaced intervals along the pipeline P. A pulling means Fis attached to heating means E to permit removal of the heating means Eduring post-installation maintenance or repair of the pipeline P.

Considering the invention in more detail, FIG. 1 illustrates oneembodiment of the pipe assembly A, which includes a pipe 12 having afluid flow passage 14 therethrough. A heater housing 16 is mounted on anupper exterior portion 18 of pipe 12 and preferably extendslongitudinally along the pipe exterior parallel to a centrallongitudinal axis 20 of pipe 12.

The heater housing 16 includes a substantially channel or C-shaped body22 and a pair of arcuate, integrally formed flanges 24 which extendcircumferentially on the exterior portion 18 of pipe 12. The flanges 24are provided to stabilize housing 16 on pipe 12 and to facilitatemounting of the housing on the pipe. Preferably, the flanges 24 arewelded to the pipe exterior, but housing 16 may be mounted with pipe 12in any convenient manner. Regardless of what mounting means is used,housing 16 is affixed to pipe 12 with the concavity of the housing body22 opening onto a pipe exterior portion 18 so that the housing body 22and pipe exterior portion 18 form a cavity 26 extending parallel to pipeaxis 20 for receiving heating means or element E. Of course, thedimensions of cavity 26 are larger than the dimensions of heatingelement E to allow the element to rest within cavity 26.

With element E operably disposed in cavity 26, fluids in flow passage ofpipe 12 are controllably heated with element E. The heating element E ispreferably an element having a pair of conductors 28 and 30 which areconnected to a source of electrical energy for resistance type heating.As shown in FIG. 1, an insulating section 32 separates the twoconductors, and a casing 34 houses the two conductors 28 and 30. Casing34 may have a flattened oval shape as shown in FIG. 1 so that thecontact area between the conductor and the pipe exterior portion 18 ismaximized. However, it should be understood that other suitable heatingelements may be used with pipe assembly A, and an element for coolingfluids in the flow passage 14 may be used in addition to or in lieu ofheating element E, depending upon the particular application in whichthe pipe assembly is employed.

In any event, it should be noted that the structure of pipe assembly Agives the assembly exceptionally good heat transfer characteristics.Heating element E is positioned immediately adjacent to the pipeexterior portion 18 and directly contacts the pipe exterior to provide amaximum common surface area between the pipe exterior and heatingelement E through which heat may be directly transferred to the pipe 12.Further, the total heat transfer area, that area of the pipe exteriorthrough which heat is transferred from the heating element to the pipeis relatively large. Unlike many prior art devices which had limitedheat transfer areas and consequently inefficient heat transfercharacteristics, the heat transfer area of apparatus A, designatedgenerally in cross-section by the heavy line 36, is equal to or greaterthan the width of heating element E so that the heat emitted by elementE is efficiently transferred through pipe 12 to flow passage 14.

The insulation layer I is mounted around the exterior of pipe 12 and theheater housing 16 mounted therewith to form an annular sleeve aroundthose elements. It extends longitudinally on assembly A to insulate pipe12 and heater housing 16 from outer environmental conditions and toensure that heat from the heating element E is transferred only in thedirection of pipe 12. The insulation layer is preformed; that is, it ismounted with assembly A as the assembly is constructed so that theassembly is transported to the pipeline installation site aspreinsulated unit. Preferably, the insulation layer I is mounted onassembly A at substantially the same time or immediately after heaterhousing 16 is mounted with pipe 12 and before element E is placed incavity 26. Generally, insulation layer I is mounted on assembly A at amanufacturing plant or other location where the assembly is beingconstructed.

In the preferred embodiment of the present invention insulation layer Iis a urethane foam or gel. A protective jacket 37 which is resistant torotting or corrosion caused by environmental conditions extends aroundinsulation layer I to protect the insulation layer and provide supportfor it. However, it should be understood that since the insulation layerI and protective jacket 37 are mounted on pipe 12 at a manufacturingplant or other construction site, conventional production techniques maybe used in constructing the insulation and jacket. Accordingly, thematerials for layer I and the method of applying of the layer andaffixing to pipe 12 may vary considerably. The use of production oftechniques not only affords latitude in the type of insulation layer Imounted with assembly A, but generally results in an insulation layer ofa quality superior to insulation which is applied at the installationsite of a pipeline. By providing preformed insulation layer I with theassemblies A of the present invention, the present invention provides apipe assembly which may be transported to the installation site as apreinsulated unit, thus eliminating the necessity of insulating pipeassemblies at the installation site, reducing the time and expendituresrequired in installing the assemblies to form pipeline, and insuringthat a better insulated assembly is used to form pipeline P.

FIG. 2 illustrates a second embodiment of pipe assembly A according tothe present invention. Except as otherwise noted below, the assemblyillustrated in FIG. 2 is substantially identical to the assembly Aillustrated in FIG. 1, and like reference numerals are used in thedrawings to indicate corresponding elements in the assemblies.

The assembly A illustrated in FIG. 2 employs a cylindrical conduit 38having a cavity 26 therethrough as the heater housing for the assemblyA. Housing 38 is mounted on an upper exterior portion 18 of pipe 12 andpreferably extends longitudinally on the pipe exterior parallel to acentral longitudinal axis 20 of pipe 12.

A plurality of bands 40 extend around pipe 12 and heater housing 38 tomount the housing 38 with pipe 12. Mounting band 40 is held taut by acrimped fastener 42. Of course, as was the case with the assembly Aillustrated in FIG. 1, any other suitable means for mounting housing 38with pipe 12 may be employed. While heater housing 38 contacts with theexterior 18 of pipe 12 only at longitudinally extending linesillustrated in the crosssectional view of FIG. 2 as 44, a heat transferadhesive means 46 bonds heater housing 38 to pipe 12 and enhances heattransfer from heating element E through heater housing 38 to theexterior portion 18 of pipe 12. The heat transfer adhesive means 46 ispreferably the type sold under the trademark "Thermon" (a trademark ofThermon Manufacturing Company of San Marcos, Tex.) and identified asThermon T-85 heat transfer cement. However, any suitable adhesive havinga high thermal conductivity may be used with apparatus A. Because of thehigh thermal conductivity of the heat transfer adhesive means 46, theeffective heat transfer area of the pipe apparatus A illustrated in FIG.2 extends throughout the entire common surface areas of the heattransfer adhesive means 46 and the pipe exterior portion 18. Line 48 inFIG. 2 illustrates a cross-sectional view of this effective heattransfer area.

As previously noted, pipe assemblies A are constructed at amanufacturing plant or other construction site and transported to thepipeline installation site as preinsulated units. The assemblies A maybe of any convenient length, but generally are as long as the standardpipe joint length of the particular type of pipe being used with theassemblies A.

Once the pipeline is at the construction site, the assemblies A arejoined together by connecting means D illustrated in FIGS. 3 and 4. Tofacilitate explanation of connecting means D, assemblies A shown in thedrawings are labeled as assemblies 50 and 52, but it should beunderstood that the assemblies are pipe assemblies A previouslydiscussed with reference to FIGS. 1 and 2. The connecting means D whichextends between assemblies 50 and 52 includes a first pipe extension 54mounted with assembly 50 and a second pipe extension 56 mounted withassembly 52. Each of the extensions 54 and 56 has a flow passageextending through it and communicating with the flow passage 14 of theassembly with which it is mounted. Preferably, the longitudinalextension of insulation layer I in jacket 37 is abbreviated on assembly50 so that pipe extension 54 is merely a protruding end of pipe 12 ofassembly 50, and the flow passage through extension 54 is a continuationof flow passage 14 of pipe 12. However, as indicated by dashed line 58denoting a weld seam, extension 54 may be a short piece of pipesubstantially identical in dimensions to pipe 12 and welded to pipe 12.The flow passage through pipe extension 54 forms an extension of flowpassage 14 through pipe assembly 50. Similarly, the portion 60 of pipeextension 56 mounted with assembly 52 may be an end portion of pipe 12extending through assembly 52. Alternatively, the entire pipe extension56 may be an integrally formed pipe extension welded or otherwisesuitably mounted with pipe 12 of assembly 52 to form a continuation offlow passage 14 through assembly 52. In either event, the portion 64 ofextension 56 extending the farthest away from assembly 52 has areceiving portion 56 with a central bore therethrough of sufficientdimensions to receive the inner portion 68 of extension 54. As can beseen from FIGS. 3 and 4, once the extensions 54 and 56 are mounted withtheir respective assemblies 50 and 52 and receiving portion 66 of pipesection 64 receives end portions 68 of extension 54, the flow passages14 through assemblies 50 and 52 are connected and communicate with oneanother through connecting means D. Extensions 54 and 56 are welded atjoint 69 or otherwise joined together.

Also illustrated in FIGS. 3 and 4 is heater housing extension means 70to form a cavity communicating with the cavities 26 formed by heaterhousing 16 of assembly 50 and by heater housing 16 of assembly 52. Theheater housing extension means 70 includes a central member 72 whichspans a substantial portion of connecting means D and two smallermounting members 74 and 76 which connect the central member 72 withheater housing 16 of the respective pipe assemblies 50 and 52. Thecentral member 72 may have a slightly arcuate shape to compensate forthe enlarged receiving section 66 of extension 64 so that the centralmember 72 is readily mountable with housing members 16. At the junctionof housing 16 and central members 72, the mounting members 74 and 76rest over the upper portions of housings 16 and central member 72.Mounting members 74 and 76 may be slightly smaller in diameter thaneither housings 16 or 72 so that once a force is exerted on the top ofthe mounting members a downward force will be exerted both on housing 16and central member 72 to force those members into firm engagement withthe pipe extensions of connecting means D. As shown in FIG. 4, amounting band 78 extends tightly around the mounting members 74 and 76to exert a downward force on the mounting members. Additional mountingbands 80 are also attached to housing 16 and central member 72 to holdthe central member 72 and housings firmly in place against theconnecting means D. Once the heater housing extension means is thussecurely mounted with connecting means D, the extension means 70 forms acavity communicating between the cavities 26 of heater housings 16 andprovides a continuous heater housing cavity through both assemblies.

With the heater housing extension means 70 and connecting means D inplace, an insulation layer indicated generally by dashed lines 82 isformed around connecting means D and heater extension means 70 so thatthe connected assemblies 50 and 52 form a fully insulated pipelinesegment. While the insulation layer 82 may be of any conventional,commercially available type for field installation, typically it is aninsulation formed in strips which are wrapped around the elements to beinsulated. The insulating layer may be composed of urethane or a varietyof other known insulating materials.

FIG. 5 illustrates a preferred embodiment of pipeline P which is formedwith connected pipe assemblies A and buried, in substantial part,beneath ground level 84. As shown, end pipe assemblies 86 and 88 areformed with a vertical elbow portion 90 so that the pipeline extendsvertically and emerges above ground level 84 at desired locations 92 and94. Other pipe assemblies may similarly be formed with horizontal elbowportions where the pipeline does not extend in a straight path betweenlocations 92 and 94.

Pipeline P may, of course, be formed with any number of assemblies A,depending on the length of the pipeline required or a particularapplication of pipeline P. Regardless of the number of assemblies used,however, the assembly pipes 12, in conjunction with the connecting meansD between them, act as a single pipe 96 and form a continuous pipelineflow passage through the entire pipeline P.

Terminal stations T positioned at or above ground level 84 are providedat spaced intervals along the length of pipeline P, and the heaterhousing 16 of assemblies A are connected to the terminal stations. Theterminal stations T - 1 provided on end pipe assemblies 86 and 88 wherepipeline P emerges from beneath ground level 84 are preferably attachedto pipe 12 of the respective assemblies at the end of housing 16 by aplurality of bolted yolks 97 (FIG. 8) or other convenient mountingmeans. For terminal stations T2 mounted at positions where pipe 96 isburied beneath ground level 84, heater housing connecting members 98 areprovided to connect heater housings 16 to the terminal stations T2.These connecting members 98 are preferably mounted on a stand pipe 100or other suitable structure to provide support for the connectingmembers and form a cavity communicating with cavity 26 of heaterhousings 16 for receiving heating element E. Thus, the housing 16extension means 70 and connecting members 98 cooperate to form apipeline heater housing 102 which forms a continuous heater cavitybetween each of the terminal stations T.

The structures of terminal stations T1 and T2 are illustrated in FIGS. 8and 6 respectively. Terminal station T1 includes a housing 104 mountedwith pipe 12 by bolted yolks 97. A doorplate not shown in FIG. 8 isprovided to permit access to the interior of the housing. A lower wall106 of housing 104 has two bores 110 and 112. Bore 112 serves as a drainto remove any moisture which might enter the interior of housing 104.Bore 110 is formed to receive an end of heating element E. Once heatingelement E is extended through bore 110 a seal made of silicone rubber orother suitable material is placed in the bore around heating element Eto prevent any moisture from seeping into heater housing 16. The portionof heater element E which extends into housing 104 is attached to aterminal block 114. A source of power is also attached to terminal block114 to provide power for actuating heating element E.

Junction station T2 shown in FIG. 6 is particularly adapted to bepositioned partially underground. An outer concrete utility box 116surrounds an inner junction box 118 and protects the inner junction box118 from the corrosive effects of the surrounding soil. As shown in FIG.5, it is preferable that utility box 116 be positioned such that anupper rim 120 extends slightly above ground level 84. Access to innerjunction box 118 is permitted through a removable cover 122 of utilitybox 116. A pair of bores 124 and 126 extend through the bases ofjunction box 118 and utility box 116 and provide an openingcommunicating with the pipeline heater housing 102 so that the heatingelement E may be extended through the bores and connected to a junctionblock 128. A source of power may also be connected to junction block 128to provide additional power for the operation of heating E. As explainedin more detail hereinbelow, pull means F which is attached to heatingelement E also extends through one or both of bores 124 and 126. If a apull means F is not provided in both bores, the bore without the pullmeans is sealed with a seal made of silicone rubber or other suitablematerial to prevent any moisture from seeping into pipeline heaterhousing 102.

As indicated above, heating element E when installed in pipeline P isremovably attached to terminal station T. It is not, however,permanently affixed to either pipe 96 or pipeline housing 102 after theassemblies A are connected and the pipeline has been completelyinsulated. Consequently, if the heating element ever needs to bereplaced or repaired, the element is simply detached from terminalstations T and pulled out of the cavity of pipeline heater housing 102using a pulling means F provided with the present invention.

To install the heating element E between two terminal stations T, aflexible line having absorbent material attached to it is first pulledthrough the pipeline housing 102. This step ensures that the cavity isdry prior to the placement of heating element E in housing 102. Next, anend of heating element E is extended a short distance into the cavittyas shown in FIG. 9. A pull line 130 is detachably connected to theheating element E with removable clamps 132. To move the element Efurther into the cavity, a force is exerted on the pull line 130 untilone of the clamps 132a nears the cavity entrance 134. The clamp nearestthe cavity entrance is then removed, and a force is again exerted on thepull line to slide the element E further into the cavity. This step ofrepeatedly pulling on the pull line 130 is continued until the element Eis extended through housing 102 to a terminal station T2.

The heating element E is then attached to terminal boxes in the terminalstations between which the element E extends, and seals are placed inthe entrances to the cavity formed by the pipeline housing 102.

To remove the heating element E after it has been installed, a pullingmeans F (FIG. 7) is attached to the heating element E upon installationof the element E, and pulling means F is positioned in bore 124 ofterminal stations T2. The pulling means F includes a washer 136 made ofinsulating material. Conductors 28 and 30 of heating element E extendthrough washer 136 and are rigidly affixed to the washer in anyconvenient manner. A pull rod 138 extends from the interior of junction118 through the washer 136 and is permanently affixed to a base 140 ofwasher 136. The pull rod 138 and conductors 28 and 30 are insulated fromeach other and bore 124 is sealed by a seal 142 which is made ofsilicone rubber or other suitable material. A pull rod handle 144 isprovided so that a force in the direction of arrow 146 is easily exertedon pull rod 138. Using pulling means F, heating element E is easilyremoved from between terminal stations T without necessitating anydamage to the pipeline insulation or other elements of the pipeline. Theelement E is first disconnected from the terminal boxes of the terminalstations T between which the element extends. A force in the directionof arrow 146 is then exerted on pull rod 138 to overcome the initialsliding resistance of element E and to pull washer 136 and a portion ofelement E out of bore 124. The remainder of element E is then pulledthrough bore 124 to complete removal of the heating element E.

From the above description of pipe assemblies A and pipeline P, it canbe seen that the present invention provides many advances in the art.The assemblies A are constructed and transported to the pipelineinstallation site as preassembled units, thus reducing pipelineinstallation expenditures and making it possible to use improvedinsulation techniques with the pipeline. Because of the structureprovided, the heating element of the pipeline is easy to install andremove after installation; yet, the heat transfer characteristics of thepipeline are excellent. Further, with terminal stations above the groundlevel and the heating means connected to the terminal stations, theheating element is always accessible at a number of locations along thepipeline for post-installation maintenance and repair.

It should be understood that the foregoing disclosure and description ofthe invention are illustrative and explanatory therof, and variouschanges in the size, shape, and materials as well as the details of theillustrated construction may be made without departing from the spiritof the invention. By way of example, but not limitation, it can be seenfrom FIG. 9 that a plurality of pipeline housings may be provided withpipe 96. Other shapes of heater housings may also be used with thepresent invention, and the heater housings may be filled with oil orother fluid to enhance heat transfer, providing the connections betweenthe housings and pipe 96 are made to be fluid tight. Additionally, itshould be noted that the pipeline P is equally well suited forinstallation above ground level, although the pipeline was describedabove as being an underground pipeline.

I claim:
 1. A preinsulated pipe assembly for handling fluid,comprising:a pipe having a fluid flow passage therethrough; a heaterhousing mounted with said pipe and forming a cavity along the exteriorof said pipe; said heater housing including a channel member mounted onthe exterior of said pipe such that said channel member and the exteriorof said pipe form said heater housing cavity; heating means disposablein said heater housing cavity for heating fluid in said flow passage ofsaid pipe; and pulling means mountable with said heating means forcontrollably pulling said heating means from said heater housing cavitywithout removal of said heater housing from said pipe.
 2. The structureset forth in claim 1, wherein:said pipe is at least partiallyunderground; and said pulling means is accessible from ground level,whereby said heating means is removable from said heater housing cavitywith said pipe and heater housing in place underground.
 3. The structureset forth in claim 1, further including:power connecting means mountedwith said pipe for connecting said heating means to an energy source foractuating said heating means.
 4. The structure set forth in claim 1,further including:mounting means for mounting said heater housing withsaid pipe.
 5. The structure set forth in claim 1, further including:aprotective layer on the exterior of said insulation layer for protectingsaid insulation layer.
 6. The structure set forth in claim 1, whereinsaid heating means has dimensions permitting said heating means to slideinto said heater housing cavity and further including:line meansdetachably connected to said heating means for exerting a force on saidheating means to slide said heating means into said heater housingcavity.
 7. A pipeline for handling fluid, comprising:a plurality ofpreinsulated pipe assemblies; each of said pipe assemblies being alignedadjacent another of said pipe assemblies and including:a pipe having afluid flow passage therethrough; a heater housing mounted with said pipeand forming a cavity along the exterior of said pipe; and a preformedinsulation layer mounted with said pipe and said heater housing; heaterhousing extension means mounted between said adjacent pipe assembliesfor forming a cavity communicating with said heater housing cavities;and connecting means for connecting said flow passage of each of saidpipe assemblies with said flow passage of said pipe assembly adjacentthereto, whereby said fluid flow passages of said pipe assemblies areconnected and form a pipeline for handling fluids.
 8. The structure setforth in claim 7, further including:terminal stations mounted at spacedintervals along said pipeline; heating means extending between saidterminal stations and disposed in said cavities of said heater housingsand said heater housing extension means for heating fluid in said flowpassages of said pipe assemblies; and said terminal stations beingmounted with selected pipe assemblies for permitting access to saidheating means disposed in said heater housing and heater housingextension means cavities.
 9. The structure set forth in claim 8, furtherincluding:pulling means mounted with said heating means for controllablypulling said heating means from said heater housing and heater housingextension means cavities, whereby said heating means is removable fromsaid cavities.
 10. The structure set forth in claim 9, wherein:saidpipeline is at least partially underground; and said pulling means isaccessible from ground level, whereby said heating means is removablefrom said cavities with said pipeline in place underground.
 11. Thestructure set forth in claim 7, wherein said connecting means includes:afirst pipe extension mounted with a first pipe assembly and having aflow passage therethrough communicating with said flow passage of saidfirst pipe assembly; a second pipe extension mounted with a second pipeassembly adjacent said first pipe assembly; and said second pipeextension having a flow passage therethrough communicating with saidflow passages through said first pipe extension and said second pipeassembly.
 12. A preinsulated pipe assembly for handling fluid,comprising:a pipe having a fluid flow passage therethrough; a heaterhousing mounted with said pipe and forming a cavity along the exteriorof said pipe; said heater housing including a cylindrical conduitmounted on the exterior of said pipe and heat transfer adhesive meansfor bonding said conduit to said pipe exterior and enhancing heattransfer from said heater housing to said pipe; a preformed insulationlayer mounted with said pipe and said heater housing for insulating saidheater housing; heating means disposable in said heater housing cavityfor heating fluid in said flow passage of said pipe; and pulling meansmountable with said heating means for controllably pulling said heatingmeans from said heater housing cavity without removal of said heaterhousing from said pipe.